Subject: Re: [PATCH 2/3] powernv:idle: Decouple TB restore & Per-core SPRs restore

From: Michael Neuling <[email-masked]>
Date: Thu, 13 Apr 2017 16:55:45 +1000

On Wed, 2017-04-12 at 17:16 +0530, Gautham R. Shenoy wrote:
> From: "Gautham R. Shenoy" <[email-masked]>
> 
> The idle-exit code assumes that if Timebase is not lost, then neither
> are the per-core hypervisor resources lost. 

Double negative!  How about:

The idle-exit code assumes that if the timebase is restored, then the
per-core hypervisor resources are also restored.

> This was true on POWER8
> where fast-sleep lost only TB but not per-core resources, and winkle
> lost both.
> 
> This assumption is not true for POWER9 however, since there can be
> states which do not lose timebase but can lose per-core SPRs.
> 
> Hence check if we need to restore the per-core hypervisor state even
> if timebase is not lost.

I think I understand what you're doing, just seems awkwardly worded.

Is this actually what the patch is doing?  It seem to be just changing one
branch.

Mikey

> 
> Signed-off-by: Gautham R. Shenoy <[email-masked]>
> ---
>  arch/powerpc/kernel/idle_book3s.S | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/idle_book3s.S
> b/arch/powerpc/kernel/idle_book3s.S
> index 9b747e9..6a9bd28 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -723,13 +723,14 @@ timebase_resync:
>  	 * Use cr3 which indicates that we are waking up with atleast partial
>  	 * hypervisor state loss to determine if TIMEBASE RESYNC is needed.
>  	 */
> -	ble	cr3,clear_lock
> +	ble	cr3,.Ltb_resynced
>  	/* Time base re-sync */
>  	bl	opal_resync_timebase;
>  	/*
> -	 * If waking up from sleep, per core state is not lost, skip to
> -	 * clear_lock.
> +	 * If waking up from sleep (POWER8), per core state
> +	 * is not lost, skip to clear_lock.
>  	 */
> +.Ltb_resynced:
>  	blt	cr4,clear_lock
>  
>  	/*